The thoracic-abdominal aneurysm is largely a progressive yielding, fatal upon breaking, of the walls of the thoracic and abdominal aorta. As there is no possible medical therapy available, the pathology can only be treated by surgical intervention, which involves a large-scale thoracic laparotomy and substitution of the dilated tract with a straight tubular prosthesis. The visceral blood vessels and sometimes the intercostal arteries are connected to the prosthesis.
The surgical operation is carried out usually according to two main techniques, often used in combination.
The first of these techniques, also known as the De Bakey method, involves clamping (hemostasis) of the tract of aorta downstream of the aneurysm, a first sectioning of the aorta itself and the suturing of the prosthesis to the first section, and the clamping of the tract of aorta upstream of the aneurysm, a second sectioning of the aorta and the suturing (anastomosis) of the prosthesis to the second section. Then the visceral branches are sutured to the prosthesis with or without interpositioning of prosthetic segments. This technique exposes the patient to quite long operations with relevant haemorrhaging, but guarantees good blood circulation downstream of the aneurysm.
The second technique, also known as the Crawford method, is based on the speed of performance of the operation. The aorta is clamped upstream and downstream of the aneurysm. The aorta is sectioned upstream and downstream of the aneurysm, hemostasis is performed on any arteries connected to the sectioned tract of aorta, and the prosthesis is applied with rapid suturing to the two sections.
The visceral and intercostal arteries from the sectioned tract of aorta are then sutured to the prosthesis, preferably without interpositioning of prosthetic segments in order not excessively to extend operation time. The technique implies that during the operation the circulation downstream of the thorax is practically stopped. If possible, in anastomosis of the visceral and intercostal arteries, patches of aortic sections surrounding the original connection points of the arteries are re-used.
Although the results obtained using the techniques are satisfactory in a majority of the cases, with the patients' progressing to full recovery, there are however not inconsiderable risks connected to the importance of the surgical operation itself. The rate of mortality during or immediately following surgery, together with post-operational respiratory difficulties and kidney failure, can reach up to 20%. There is also a risk of about 20% of paraplegia, leading many patients to refuse to undertake the operation.
Paraplegia, as well as the other complications, is essentially due to a blockage in arterial circulation to the lower parts of the body. This blockage, which is of a length correlated to the difficulty of performance of the operation, can obviously lead to medullar ischemia and therefore to paralysis of the lower limbs.
To limit the risk of paraplegia temporary aortic by-passes are used, with extracorporeal circulation tubing taking blood from upstream of the aneurysm and sending it to the lumbar and hypogastric arteries. The inflow of blood to these arteries guarantees a sufficient vascularization of the medulla and the abdominal organs, very considerably reducing risks of ischemia. The use of extracorporeal circulation, however, involves considerable use of anticoagulants, especially if a pump is used, as is sometimes the case; in all cases, however, long operation times are needed.